With development of wireless communication technology, at present, a mobile phone has been developed on a type which may read two Subscriber Identity Module (SIM) cards. Because the SIM card is electrically connected to a circuit board via an electrical connector, in order to meet the requirement on the connector which may mate with two SIM cards at the same time and reduce a surface area of the circuit board occupied by itself, a stack-type SIM card connector is proposed, as disclosed in Taiwanese utility model patent publication No. TWM324877 (corresponding to Chinese patent grant Publication No. CN201081824Y).
In the electrical connector as disclosed in the above patent, a first housing and a second housing (which are formed of an insulative material) which are engaged in a vertical direction and a shield together define two card insertion spaces respectively positioned in an upper layer and a lower layer. However, because the second housing in the lower layer has a larger surface area, when the electrical connector is connected to a circuit board by means of reflow, the second housing is easy to warp due to heat so that the whole coplanarity of the second housing is reduced. Moreover, during reflow, the second housing is subjected to more heat than the first housing, and thus the warping potential of the second housing is larger than that of the first housing, thereby resulting in that assembly of the first housing and the second insulative becomes tight, and the first housing and the second insulative will affect on each other in warpage and coplanarity after reflow, which results in that the quality of the electrical connector is not stable. Moreover, obviously, the design of the second housing itself is more complicated, which requires more cost in material and manufacturing process.